We're here to discuss his latest film - to give it its full title, Birdman or (The Unexpected Virtue Of Ignorance).

Keaton plays Riggan, an actor who hopes to revive his flagging career by directing and starring in an ambitious Broadway production of a play he has also re-written himself.

Riggan is riddled with self-doubt and a fear of failure. As a result, his sub-conscious has started to speak to him in the voice of his former character Birdman; the superhero role that made him famous, whose poster looms over his dressing room.

The film is a brilliant satire on a film industry dominated by blockbuster comic book sequels. It is both darkly thought-provoking and laugh-out-loud funny. Edward Norton, Emma Stone, Naomi Watts and Zach Galifianakis all give notable performances.

And it invites audiences behind the scenes of the acting world - showing the human frailty behind celebrity.

"It was fun to play, but at the same time, this movie's tricky - you can't enjoy it while you're doing it," confesses Pennsylvania-born Keaton.

"It's odd. You really enjoy it, but it was so hard to do these scenes."

One of the comic highlights is when Riggan pops out for a cigarette between scenes and the stage door blows shut, trapping his dressing gown.

The fragile actor is forced to run around the side of theatre and through Times Square to get back in through the front of the theatre - wearing only in his underpants.

It was filmed on location, so Keaton ran almost naked through one of the most crowded parts of New York, while people pointed and filmed it on their phones.

"It was really weirdly fun," he adds of filming the scene. "It's fun to play a guy who's this screwed up. To literally get naked, I guess, I didn't think I'd enjoy it so much."

The parallels between Keaton and Riggan are obvious. The 63-year-old began acting on TV in the 70s. In 1988, he starred in Tim Burton's dark family comedy Beetlejuice, and a year later, the director cast him as the Caped Crusader in his film adaptation of Batman.

Since then, Keaton's kept making movies. He had a role in Tarantino's Jackie Brown, some successful comedies, voice work in hit animations Cars and Toy Story 3, but Batman has remained the peak of his career. So does he relate to Riggan's scenario?

"Oh no, no, no," he insists.

"Obviously, I relate to him in, 'Oh yeah, I played Batman', he plays a character called Birdman, it's not coincidental," he adds quickly. "I'd be insane if I didn't go, 'Yeah, I did that too'.

"I relate to how sometimes you feel good, sometimes you don't feel so good. Sometimes you feel secure, sometimes you don't feel so secure."

If Keaton had ever felt as insecure and down about his own career as Riggan, he certainly has no need to now.

buzz

The film has already begun garnering awards, and the industry is all atwitter with Oscar buzz for Birdman.

When Keaton played Batman, Hollywood stars were still treated as real superheroes. Fans looked up to them and respected them.

Now, the insatiable appetite for internet gossip seems to make them a target. Tear them down from their pedestal and expose them for what they really are - flawed human beings, just like the rest of us.

"I wonder if people always did that?" muses Keaton, with the voice of one who knows.

"Anyway, it's more so now, because of technology. You can catch people looking horrible or doing things that they actually do. It's more intense now than ever."

But he doesn't seem that bothered, and why should he be? Keaton doesn't need to worry about having his mask ripped off, because he's not hiding behind one.

And while for some, he will always be Batman, soon he is sure to have some awards to put on the shelf next to the superhero memorabilia.

Keaton is an actor, and in Birdman, he is a superb one.

Birdman is out in cinemas now